Here's a final quote from the paper which I think is succinct.

"The blues form itself developed with the prison experience at its core, explicitly in songs such as "Penal Farm Blues," "Mississippi Jail House Groan," "My Home Is a Prison," "Heah I Am In Dis Low-Down Jail," and the many different songs entitled "Prison Blues," "Jailhouse Blues," and "Chain Gang Blues." Many of the finest artists were prisoners or ex-prisoners: Charley Patton, Cow Cow Davenport, Robert Pete Williams, Texas Alexander, Son House, Willie Newbern, and, of course, Lightnin' Hopkins (whose ankles bore the scars of chain gang shackles), Leadbelly, and Billie Holiday."